Method and apparatus for investigating a borehole with a caliper

ABSTRACT

Embodiments of the present invention relate to a caliper and method for mapping the dimensions and topography of a formation such as the sidewall of a borehole. Examples of formations in which embodiments of the invention can be used include, but are not limited to, an oil, gas, pile borehole or barrette that has been drilled or excavated into the earth.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 16/289,115, filed Feb. 28, 2019; which is a continuation ofU.S. patent application Ser. No. 15/823,113, filed Nov. 27, 2017; whichis a continuation of U.S. patent application Ser. No. 14/978,743 filedDec. 22, 2015, which is a continuation of U.S. patent application Ser.No. 12/353,648, filed Jan. 14, 2009, now U.S. Pat. No. 9,217,324; whichis a continuation of U.S. patent application Ser. No. 11/641,356, filedDec. 18, 2006, now U.S. Pat. No. 7,495,995; which claims the benefit ofU.S. Provisional Patent Application Ser. No. 60/751,361, filed Dec. 16,2005; all of which are hereby incorporated by reference herein in theirentirety, including any figures, tables, or drawings.

BACKGROUND OF INVENTION

When formations such as boreholes are drilled or otherwise created intoearth, the actual shape of the formation, including dimensions and/ortopology, can be useful information to have prior to filling theformation. The formation can be filled with, for example, concreteand/or other materials to form a pile or other structure. As such pilesare often used to form the foundations of buildings or other largestructures. As such the piles are often tested to determine theload-bearing capacity of the pile and the tests typically involve theincorporation of a device for performing testing. The shape of thecross-section of the pile in the region of the pile where the testdevice is positioned can enhance the accuracy of the interpretation ofthe data from the test device. In addition, the shape of formation canbe useful to determine if there are any major irregularities and/ordetermine the potential interaction between the pier and the sides ofthe formation when a load is applied. In addition, the accumulation ofcross-sectional shapes can be used to calculate the volume of theformation.

Techniques for providing information regarding the shape of formationshave included lowering a sonar device in the formation and obtaining twoor more vertical lines of sonar readings along the walls of theformation. However, such limited information can miss importantirregularities in the sides of the formation. In addition, data fromregions of the formation having dirty fluids can be difficult toaccurately interpret. In fact, the radial diameters of the formations inregions with dirty fluids can appear narrower than they actually are dueto the effects of the particulates in the fluid on the sonar signals.

Accordingly, there is a need in the art for a method and apparatus thatcan provide accurate information regarding the dimensions and/ortopology of a formation such as a borehole, especially when theformation is filled with opaque stabilizing fluids whose density oftenvaries with depth.

BRIEF SUMMARY

Embodiments of the present invention relate to a caliper and method formapping the dimensions and topography of a formation such as thesidewall of a borehole. Examples of formations in which embodiments ofthe invention can be used include, but are not limited to, an oil, gas,pile borehole or barrette that has been drilled or excavated into theearth. Such dimensional and topographic information can allow moreaccurate interpretation of test devices positioned in the pile createdwithin the borehole and can allow an accurate determination of thevolume of concrete needed to fill the pile. Such information can alsoallow more accurate projections of the interaction of the side of thepile with the side of the borehole, especially when the formation isfilled with opaque stabilizing fluids whose density often varies withdepth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a borehole with anembodiment of a caliper in accordance with the present invention in theborehole.

DETAILED DISCLOSURE OF THE INVENTION

Embodiments of the present invention relate to a caliper and method formapping the dimensions and topography of a formation such as thesidewall of a borehole. Examples of formations in which embodiments ofthe invention can be used include, but are not limited to, an oil, gas,pile borehole or barrette that has been drilled or excavated into theearth. Such dimensional and topographic information can allow moreaccurate interpretation of test devices positioned in the pile createdwithin the borehole and can allow an accurate determination of thevolume of concrete needed to fill the pile. Such information can alsoallow more accurate projections of the interaction of the side of thepile with the side of the borehole.

FIG. 1 shows one embodiment of caliper 10 suspended in borehole 12 bycable 14. Borehole 12 penetrates earth formation 16. One or more guidecables 18 can also be suspended down into borehole 12. In oneembodiment, two guide cables 18 are parallel to each other and areweighted 42 to fall plumb into borehole 12. In one embodiment, one ormore cables 14, 18 include a conductor for transmitting commands and/orpower to caliper 10 and for receiving data back from caliper 10. Caliper10 can be raised and lowered on cable 14 by draw works 20, movingslidably along guide cables 18. Guide cables 18 are raised and loweredindependently of cable 14, by draw works 22. In one embodiment, allguide cables 18 are coordinated by being raised and lowered by a singledraw work assembly 22. Draw works 20, 22 can be of any type known in theart, including pulley systems. Draw works 20, 22 are typically installedat ground level 24. In an embodiment, draw works 20 and 22 are connectedto a common frame structure. In further embodiments, draw works 20 and22 can be such that the raising and lowering of a plurality of cables 18is in unison.

In one embodiment, guide cables 18 are suspended independently of cable14, which carries caliper 10. This arrangement allows for greaterpositional control of guide cables 18. Positional control of guidecables 18 is desirable for preventing contact between caliper 10 andinterior wall 26 of borehole 12 as caliper 10 descends and ascends,guided by guide cables 18. Positioning guide cables 18 in borehole 12and then lowering caliper 10 as caliper 10 is guided by guide cable 18can allow a more accurate determination of the position of caliper 10.In an alternative embodiment, cable 14 can be removed and caliper 10 canincorporate means for moving caliper 10 to propel itself up and down bygripping on cables 18. Means for propelling up and down a cable areknown in the art and can be incorporated in caliper 10 for this purpose.In additional embodiments, caliper 10 can be fixably attached to one ormore cables 18 and the caliper 10 lowered by lowering cable 18 to whichthe caliper is fixably attached and/or enabling caliper 10 to travelwith respect to one or more cable 18 to which the caliper 10 is notfixably attached. In another embodiment, caliper 10 can incorporate agyroscopic stabilizer and an internal compass to allow the caliper 10 tobe raised and lowered without the use of guide cables 18.

Caliper 10 is insertable into opening 28 of borehole 12 and can includesonar head 30 for transmitting acoustical energy toward interior wall 26of borehole 12. When the acoustic energy reaches interior wall 26 theacoustic waves are reflected by interior wall 26 back to sonar head 30.Sonar head 30 detects the acoustic waves and measures the elapsed timebetween transmission of the acoustical energy and detection of theacoustic waves. From elapsed time measurements, the distance from thesonar head to the interior wall and back in a certain direction can bedetermined, allowing determination of the location of interior wall 26relative to sonar head 30. Additional embodiments can incorporate alight source, such as a laser source. This laser source can be usedinstead of the sonar head 30 or in conjunction with sonar head 30. Thelaser source can transmit a light beam toward interior wall 26 that canbe reflected by interior wall 26 and detected by caliper 10. Again, bymeasuring the elapsed time between transmission and detection of thelight, the distance from the laser source to the interior wall 26 in acertain direction can be determined, allowing determination of thelocation of the interior wall 26.

In one embodiment, caliper 10 includes a motor (not shown). In oneembodiment, caliper 10 includes gears and shafts for enabling the motorto rotate sonar head 30. In various embodiments, caliper 10 can includeone or more of the following; gyroscope stabilizer 32, internalinclinometer 34, internal compass 36, and pressure measuring device. Apressure measuring device can measure the pressure of the caliper'senvironment in the fluid in the formation, where the pressure is afunction of the depth and density of the fluid and can, for example, beused to provide the density of the fluid when the depth is known. In oneembodiment, as caliper 10 is raised or lowered in borehole 12, currentis supplied to the motor via cable 14 which connects caliper 10 to agenerator (not shown) on ground level 24. Other electrical signals cantravel down cable 14 and/or cable 18. In one embodiment, sonar head 30is rotated by the motor as caliper 10 advances along borehole axis 38.Acoustic pulses emitted from sonar head 30 along borehole radius 40 canscan borehole wall surfaces 26 with such pulses emitted either as thecaliper 10 with sonar head 30 is continuously raised or lowered, or atmultiple fixed depths of the borehole that the sonar head 30 issequentially raised or lowered to. By rotating sonar head 30 as thecaliper 10 is raising or lowering, a spiral or helical pattern ofmeasurements can be accomplished, while allowing continuous movement ofthe caliper 10 and the sonar head.

The speed of the caliper 10 raising or lowering can be varied with timewhen, for example, it is desired to have more or fewer measurements of acertain portion of the borehole. Likewise, the rotation speed of thecaliper head 10 can vary with time if, for example, it is desired tohave more or fewer measurements of a certain portion of the borehole. Aportion of the energy from each acoustic pulse, or laser pulse, isreflected by wall surface 26 of borehole 12 along radius 40 back towardsonar head 30, which detects the reflected energy. The reflectionscontain information relating to the topographic features and contours ofwalls 26 of borehole 12. The number of measurements per unit area ofbore hole wall 26 can be controlled by controlling the speed of raisingand/or lowering sonar head 30 and/or controlling the rotation speed ofsonar head 30. In an embodiment, sonar head 30 rotates one full rotationbetween advancement intervals of caliper 10 along borehole axis 38. Inthis case, information is gathered in planar fields at discretelocations along axis 38.

In one embodiment, electronic modules (not shown) on ground level 24transmit operating commands down borehole 12 and in return, receivesdata back that may be recorded on a storage medium of any desired typefor concurrent or later manual or automated processing. Data processormeans, such as a suitable computer, may be provided for performing dataanalysis in the field in real time. In addition or in the alternative,the recorded data may be sent to a processing center for post processingof the data.

Because borehole 12 may contain a fluid that changes in density withchanges in depth or other position, caliper 10 can be calibrated to takethese changes into effect. In one embodiment, because the distancebetween sonar head 30 and each guide cable 18 is known and constantduring a particular operation, a pulse can be directed at a guide cable18 and the time lapse between transmission and detection measured.Changes in return speed at different positions along axis 38 can be usedto calibrate caliper 10 to take fluid properties into account to improvethe accuracy of the measurement of the distance from the sonar head 30to the walls 26. In an embodiment, a pulse can be reflected from cable18 for each rotation of the sonar head 30 to provide calibration of thespeed of sound and/or light in the surrounding material for that depth.In another embodiment, a sonar pulse and a laser pulse can be reflectedfrom a known location on or near the walls 26 and the difference in thespeed of sound and the speed of light in the surrounding material can beused to calibrate the measurement results for the surrounding material.

In one embodiment, multiple excitation frequencies are available fromwhich the operator can choose, depending on factors such as the type andproperties of fluid in borehole 12. The choice of excitation frequencyis a compromise between the need for signal penetration through theborehole fluid using a longer-wavelength, lower frequency pulse, moreacoustic energy (the borehole fluid can have undesirably attenuatingeffects at higher pulse frequencies) and the need for spatial resolutionthat is achievable using shorter wavelengths albeit at the expense ofhigher signal transmission losses. Embodiments can utilize multiplefrequencies during the same measurement. A specific embodiment of theinvention pertains to measuring the physical characteristics of aborehole having a diameter between 1.5 feet and 20 feet, and in anotherembodiment between 3 feet and 12 feet. In one specific embodiment, anexcitation frequency in the range 50 kHz-300 kHz is used; in anotherspecific embodiment, an excitation frequency in the range 500 kHz-800kHz is used; and in a further specific embodiment, an excitationfrequency in the range 1.0 MHz-1.5 MHz is used.

In one embodiment, an inclinometer 42, can be attached to the end, orother location, of cable 18, rather than merely weights. Thus, if guidecables 18 are not able to hang freely, inclinometers 42 can provide anoutput signal indicative of the orientation of the end of each guidecable 18 in the borehole 12. This situation may be encountered whereborehole 12 is not sufficiently vertical, with respect to gravity, forexample.

EMBODIMENTS Embodiment 1

An apparatus for investigating a formation, comprising:

a caliper adapted to be lowered into a formation such that an axis ofthe caliper is substantially parallel with the longitudinal axis of theformation, wherein the caliper comprises:

a transmitter for transmitting a transmitted pulse signal;

a detector for detecting a reflected pulse signal, wherein the reflectedpulse signal is the transmitted pulse signal reflected from a targetlocation on a surface of the formation onto which the transmitted pulsesignal is incident;

a means for determining the time interval between the transmission ofthe transmitted pulse signal and the detection of the reflected pulsesignal, wherein the distance from the transmitter to the target locationon the surface of the formation and back to the detector is the timeinterval between the transmission of the transmitted pulse signal andthe detection of the reflected pulse signal times the speed of the firstpulse signal;

a means for rotating the transmitter and the detector with respect tothe axis of the caliper, wherein rotation of the transmitter and thedetector causes the target location on the surface of the formation ontowhich the transmitted pulse signal is incident to rotate with respect tothe axis of the caliper.

Embodiment 2

The apparatus according to Embodiment 1, wherein the formation is aborehole.

Embodiment 3

The apparatus according Embodiment 1, further comprising:

a means for raising and lowering the caliper in the formation, whereinraising and lowering the caliper in the formation causes the targetlocation on the surface of the formation to raise and lower,respectively.

Embodiment 4

The apparatus according Embodiment 3, further comprising:

a means for controlling the rotation of the transmitter and detector andthe raising and lowering of the caliper such that the first pulse signalis incident on a plurality of target locations on the surface of theformation, and a means for producing a representation of a portion ofthe formation corresponding to the plurality of target locations on thesurface of the formation onto which the transmitter signal is incident.

Embodiment 5

The apparatus according to Embodiment 3, further comprising:

one or more guide cables for guiding the caliper as the caliper israised and/or lowered in the formation, wherein the one or more guidecables allow the position of the caliper to be controlled as the caliperis raised and/or lowered in the formation.

Embodiment 6

The apparatus according to Embodiment 1, wherein the transmittercomprises a laser light source.

Embodiment 7

The apparatus according to Embodiment 1, wherein the transmittercomprises a sonar head.

Embodiment 8

The apparatus according to Embodiment 5, wherein the one or more guidecables are weighted to fall plumb into the formation.

Embodiment 9

The apparatus according to Embodiment 8, wherein at least one of the oneor more guide cables is weighted with an inclinometer for providing anoutput signal indicative of the orientation of the at least one guidecable.

Embodiment 10

The apparatus according to Embodiment 5, further comprising a means forraising and/or lowering the caliper up and down the at least one of theone or more guide cables by gripping on the at least one guide cable.

Embodiment 11

The apparatus according to Embodiment 5, wherein the caliper is attachedto at least one of the one or more guide cables, wherein the means forraising and lowering the caliper comprises a means for raising andlowering the at least one guide cable attached to the caliper such thatraising and lowering the at least one guide cable attached to thecaliper raises and lowers the caliper.

Embodiment 12

The apparatus according to Embodiment 5, wherein the means for raisingand lowering the caliper comprises a cable attached to the caliper.

Embodiment 13

The apparatus according to Embodiment 10, wherein one or more of the oneor more guide cables and the cable comprise a conductor for transmittingcommands and/or power to the caliper and for receiving data back fromcaliper.

Embodiment 14

The apparatus according to Embodiment 1, wherein the caliper furthercomprises a compass.

Embodiment 15

The apparatus according to Embodiment 1, wherein the caliper furthercomprises a gyroscopic stabilizer.

Embodiment 16

The apparatus according to Embodiment 1, further comprising a means fordetermining the speed of the transmitted pulse signal.

Embodiment 17

The apparatus according to Embodiment 16, wherein the means fordetermining the speed of the transmitted pulse signal comprises anobject a known distance from the transmitter wherein the speed of thetransmitted pulse signal is the distance from the transmitter to theobject and back to the detector divided by the time interval between thetransmission of the transmitted pulse signal and the detection of thereflected pulse signal from the object.

Embodiment 18

The apparatus according to Embodiment 7, wherein the sonar headtransmits in the range 50 kHz-300 kHz.

Embodiment 19

The apparatus according to Embodiment 7, wherein the sonar headtransmits in the range 500 kHz-800 kHz.

Embodiment 20

The apparatus according to Embodiment 7, wherein the sonar headtransmits in the range 1.0 MHz-1.5 MHz.

Embodiment 21

The apparatus according Embodiment 1, further comprising a means fordetermining the density of a fluid the transmitted pulse signal travelsinto the target location.

Embodiment 22

The apparatus according to Embodiment 21, wherein the means fordetermining the density of the fluid the transmitted pulse signaltravels in comprises a pressure measuring device.

Embodiment 23

The apparatus according to Embodiment 1, wherein the caliper furthercomprises an inclinometer.

Embodiment 24

An method for investigating a formation, comprising:

positioning a caliper into a formation such that an axis of the caliperis substantially parallel with the longitudinal axis of the formation,

transmitting a transmitted pulse signal from a transmitter on thecaliper;

detecting a reflected pulse signal with a detector on the caliper,wherein the reflected pulse signal is the transmitted pulse signalreflected from a target location on a surface of the formation ontowhich the transmitted pulse signal is incident;

determining the time interval between the transmission of thetransmitted pulse signal and the detection of the reflected pulsesignal, wherein the distance from the transmitter to the target locationon the surface of the formation and back to the detector is the timeinterval between the transmission of the transmitted pulse signal andthe detection of the reflected pulse signal times the speed of the firstpulse signal;

rotating the transmitter and the detector with respect to the axis ofthe caliper, wherein rotation of the transmitter and the detector causesthe target location on the surface of the formation onto which thetransmitted pulse signal is incident to rotate with respect to the axisof the caliper.

Embodiment 25

The method according to Embodiment 24, wherein the formation is aborehole.

Embodiment 26

The method according Embodiment 24, further comprising:

raising and lowering the caliper in the formation, wherein raising andlowering the caliper in the formation causes the target location on thesurface of the formation to raise and lower, respectively.

Embodiment 27

The method according Embodiment 26, further comprising:

controlling the rotation of the transmitter and detector and the raisingand lowering of the caliper such that the first pulse signal is incidenton a plurality of target locations on the surface of the formation, andproducing a representation of a portion of the formation correspondingto the plurality of target locations on the surface of the formationonto which the transmitter signal is incident.

Embodiment 28

The method according to Embodiment 26, further comprising:

guiding the caliper on one or more guide cables as the caliper is raisedand/or lowered in the formation, wherein the one or more guide cablesallow the position of the caliper to be controlled as the caliper israised and/or lowered in the formation.

Embodiment 29

The method according to Embodiment 24, wherein the transmitter comprisesa laser light source.

Embodiment 30

The method according to Embodiment 24, wherein the transmitter comprisesa sonar head.

Embodiment 31

The method according to Embodiment 28, wherein the one or more guidecables are weighted to fall plumb into the formation.

Embodiment 32

The method according to Embodiment 31, wherein at least one of the oneor more guide cables is weighted with an inclinometer for providing anoutput signal indicative of the orientation of the at least one guidecable.

Embodiment 33

The method according to Embodiment 28, further comprising raising and/orlowering the caliper up and down the at least one of the one or moreguide cables by gripping on the at least one guide cable.

Embodiment 34

The method according to Embodiment 28, wherein the caliper is attachedto at least one of the one or more guide cables, wherein raising andlowering the caliper comprises raising and lowering the at least oneguide cable attached to the caliper such that raising and lowering theat least one guide cable attached to the caliper raises and lowers thecaliper.

Embodiment 35

The method according to Embodiment 28, wherein raising and lowering thecaliper comprises raising and lowering the caliper via a cable attachedto the caliper.

Embodiment 36

The method according to Embodiment 33, further comprising transmittingcommands and/or power to the caliper and for receiving data back fromcaliper via a conductor in one or more of the one or more guide cablesand/or the cable.

Embodiment 37

The method according to Embodiment 24, wherein the caliper furthercomprises a compass.

Embodiment 38

The method according to Embodiment 24, wherein the caliper furthercomprises a gyroscopic stabilizer.

Embodiment 39

The method according to Embodiment 24, further comprising determiningthe speed of the transmitted pulse signal.

Embodiment 40

The method according to Embodiment 39, wherein determining the speed ofthe transmitted pulse signal comprises positioning an object a knowndistance from the transmitter wherein the speed of the transmitted pulsesignal is the distance from the transmitter to the object and back tothe detector divided by the time interval between the transmission ofthe transmitted pulse signal and the detection of the reflected pulsesignal from the object.

Embodiment 41

The method according to Embodiment 30, wherein the sonar head transmitsin the range 50 kHz-300 kHz.

Embodiment 42

The method according to Embodiment 30, wherein the sonar head transmitsin the range 500 kHz-800 kHz.

Embodiment 43

The method according to Embodiment 30, wherein the sonar head transmitsin the range 1.0 MHz-1.5 MHz.

Embodiment 44

The method according Embodiment 24, further comprising determining thedensity of a fluid the transmitted pulse signal travels into the targetlocation.

Embodiment 45

The method according to Embodiment 44, wherein determining the densityof the fluid the transmitted pulse signal travels in comprises measuringthe pressure in the fluid the transmitted pulse signal travels in.

Embodiment 46

The method according to Embodiment 24, wherein the caliper furthercomprises an inclinometer.

Embodiment 47

The method according to Embodiment 24, wherein the formation has adiameter in the range 1.5 feet to 20 feet.

Embodiment 48

The method according to Embodiment 24, wherein the formation has adiameter in the range 3 feet to 12 feet.

All patents, patent applications, provisional applications, andpublications referred to or cited herein are incorporated by referencein their entirety, including all figures and tables, to the extent theyare not inconsistent with the explicit teachings of this specification.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to a person skilled in theart and are to be included within the spirit and purview of thisapplication. For example, while the use of sonar energy has beendescribed, it is contemplated that the apparatus and method can beadapted to use laser energy, for example.

What is claimed is:
 1. An apparatus for investigating a formation,comprising: a caliper adapted to be lowered into a formation such thatan axis of the caliper is substantially parallel with the longitudinalaxis of the formation, wherein the caliper comprises: a transmitter fortransmitting a transmitted pulse signal; a detector for detecting areflected pulse signal, wherein the reflected pulse signal is thetransmitted pulse signal reflected from a target location on a surfaceof the formation onto which the transmitted pulse signal is incident; ameans for determining the time interval between the transmission of thetransmitted pulse signal and the detection of the reflected pulsesignal, wherein the distance from the transmitter to the target locationon the surface of the formation and back to the detector is the timeinterval between the transmission of the transmitted pulse signal andthe detection of the reflected pulse signal times the speed of the firstpulse signal; and a means for rotating the transmitter and the detectorwith respect to the axis of the caliper, wherein rotation of thetransmitter and the detector causes the target location on the surfaceof the formation onto which the transmitted pulse signal is incident torotate with respect to the axis of the caliper.
 2. The apparatusaccording to claim 1, wherein the formation is a borehole.
 3. Theapparatus according to claim 1, further comprising: a means for raisingand lowering the caliper in the formation, wherein raising and loweringthe caliper in the formation causes the target location on the surfaceof the formation to raise and lower, respectively.
 4. The apparatusaccording claim 3, further comprising: a means for controlling therotation of the transmitter and detector and the raising and lowering ofthe caliper such that the first pulse signal is incident on a pluralityof target locations on the surface of the formation; and a means forproducing a representation of a portion of the formation correspondingto the plurality of target locations on the surface of the formationonto which the transmitter signal is incident.
 5. The apparatusaccording to claim 3, further comprising: one or more guide cables forguiding the caliper as the caliper is raised and/or lowered in theformation, wherein the one or more guide cables allow the position ofthe caliper to be controlled as the caliper is raised and/or lowered inthe formation.
 6. The apparatus according to claim 1, wherein thetransmitter comprises a laser light source.
 7. The apparatus accordingto claim 1, wherein the transmitter comprises a sonar head.
 8. Theapparatus according to claim 5, wherein the one or more guide cables areweighted to fall plumb into the formation.
 9. The apparatus according toclaim 8, wherein at least one of the one or more guide cables isweighted with an inclinometer for providing an output signal indicativeof the orientation of the at least one guide cable.
 10. The apparatusaccording to claim 5, further comprising: a means for raising and/orlowering the caliper up and down the at least one of the one or moreguide cables by gripping on the at least one guide cable.
 11. Theapparatus according to claim 5, wherein the caliper is attached to atleast one of the one or more guide cables, and wherein the means forraising and lowering the caliper comprises: a means for raising andlowering the at least one guide cable attached to the caliper such thatraising and lowering the at least one guide cable attached to thecaliper raises and lowers the caliper.
 12. The apparatus according toclaim 5, wherein the means for raising and lowering the calipercomprises: a cable attached to the caliper.
 13. The apparatus accordingto claim 10, wherein one or more of the one or more guide cables and thecable comprise: a conductor for transmitting commands and/or power tothe caliper and for receiving data back from caliper.
 14. The apparatusaccording to claim 1, wherein the caliper further comprises: a compass.15. The apparatus according to claim 1, wherein the caliper furthercomprises: a gyroscopic stabilizer.
 16. The apparatus according to claim1, further comprising: a means for determining the speed of thetransmitted pulse signal.
 17. The apparatus according to claim 16,wherein the means for determining the speed of the transmitted pulsesignal comprises an object a known distance from the transmitter, andwherein the speed of the transmitted pulse signal is the distance fromthe transmitter to the object and back to the detector divided by thetime interval between the transmission of the transmitted pulse signaland the detection of the reflected pulse signal from the object.
 18. Theapparatus according to claim 7, wherein the sonar head transmits in therange 50 kHz-300 kHz.
 19. The apparatus according to claim 7, whereinthe sonar head transmits in the range 500 kHz-800 kHz.
 20. A method forinvestigating a formation, comprising: positioning a caliper into aformation such that an axis of the caliper is substantially parallelwith the longitudinal axis of the formation; transmitting a transmittedpulse signal from a transmitter on the caliper; detecting a reflectedpulse signal with a detector on the caliper, wherein the reflected pulsesignal is the transmitted pulse signal reflected from a target locationon a surface of the formation onto which the transmitted pulse signal isincident; determining the time interval between the transmission of thetransmitted pulse signal and the detection of the reflected pulsesignal, wherein the distance from the transmitter to the target locationon the surface of the formation and back to the detector is the timeinterval between the transmission of the transmitted pulse signal andthe detection of the reflected pulse signal times the speed of the firstpulse signal; and rotating the transmitter and the detector with respectto the axis of the caliper, wherein rotation of the transmitter and thedetector causes the target location on the surface of the formation ontowhich the transmitted pulse signal is incident to rotate with respect tothe axis of the caliper.